[20190322]测试相同语句遇到导致cursor pin S的疑问.txt

--//昨天测试遇到的情况,链接:http://blog.itpub.net/267265/viewspace-2638857/
--//我一直认为打散sql语句,避开cursor: pin S等待事件,能够提高执行效率.而测试结果有点出乎意料.
--//反而是测试2快于测试1,很难理解为什么会出现这样的情况,今天继续探究看看.

1.环境:
SCOTT@book> @ ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

2.建立测试脚本:
create table job_times (sid number, time_ela number,method varchar2(20));

$ cat m1.txt
set verify off
insert into job_times values ( sys_context ('userenv', 'sid') ,dbms_utility.get_time ,'&&2') ;
commit ;
declare
v_id number;
v_d date;
begin
    for i in 1 .. &&1 loop
        select /*+ &&3 */ 1 into v_id from dual ;
        --select /*+ &&3 */ sysdate into v_d from dual ;
    end loop;
end ;
/
update job_times set time_ela = dbms_utility.get_time - time_ela where sid=sys_context ('userenv', 'sid') and method='&&2';
commit;
quit

$ cat m2.txt
set verify off
insert into job_times values ( sys_context ('userenv', 'sid') ,dbms_utility.get_time ,'&&2') ;
commit ;
declare
v_id number;
v_d date;
begin
    for i in 1 .. &&1 loop
        select  1 into v_id from dual ;
        --//select  sysdate into v_d from dual ;
    end loop;
end ;
/
update job_times set time_ela = dbms_utility.get_time - time_ela where sid=sys_context ('userenv', 'sid') and method='&&2';
commit;
quit

--//通过加入注解&&3,产生每个会话执行语句不同,对比看看.昨天的测试第2种情况快于第1种情况,不理解,我再次重复测试:

3.测试:
--//测试最好避开整点的awr生成以及其它对数据库的操作,
seq 1 40 | xargs -I {}  echo 'seq {} | xargs -I %#  -P {} bash -c  "sqlplus -s -l scott/book @m1.txt 1e6 m1_{} %# >/dev/null"' | bash
seq 1 40 | xargs -I {}  echo 'seq {} | xargs -I %#  -P {} bash -c  "sqlplus -s -l scott/book @m2.txt 1e6 m2_{} %# >/dev/null"' | bash

$ sqlplus -s -l scott/book <<< "select method,count(*),round(avg(TIME_ELA),0),sum(TIME_ELA) from job_times where method like 'm%' group by method order by to_number(substr(method,4)),4;" | egrep "^|m1_.*$"
METHOD COUNT(*) ROUND(AVG(TIME_ELA),0) SUM(TIME_ELA)
------ -------- ---------------------- -------------
m2_1          1                   1802          1802
m1_1          1                   1841          1841
m1_2      &n